Method for Monitoring a Steering Device

ABSTRACT

A method for monitoring a steering device including a steering gear, a first steering actuator, a second steering actuator, a first traction mechanism drive with a first traction mechanism configured to connect the first steering actuator to the steering gear, and a second traction mechanism drive with at least one second traction mechanism configured to connect the second steering actuator to the steering gear, includes determining at least one first position parameter of the first steering actuator, and at least one second position parameter of the second steering actuator. The method includes evaluating the first position parameter and the second position parameter to determine that an unintentional change in position of at least one of the first traction mechanism and the second traction mechanism has occurred, and definitely associating the unintentional change in position with one of the first and second traction mechanism drives.

PRIOR ART

The invention is based on a method for monitoring a steering deviceaccording to the generic term of claim 1. In addition, the inventionrelates to a control unit with a computing unit for carrying out such amethod and a steering device with a computing unit for carrying out sucha method.

From the prior art, for example DE 100 52 275 A1, steering devices areknown which comprise a steering gear, at least one first electric motor,at least one second electric motor, at least one first belt drive forconnecting the first electric motor to the steering gear and at leastone second belt drive for connecting the second electric motor to thesteering gear. Such steering devices are, for example, used inredundant, conventional steering systems with mechanical feedthroughbetween the steering wheel and the steering gear, in so-calledsteer-by-wire steering systems without mechanical feedthrough betweenthe steering wheel and the steering gear and/or in steering systems forcommercial vehicles with electric steering support.

With the use of belt drives or other traction mechanism drives, however,there is the problem that in operation and under certain conditionsunintentional changes in position of the traction mechanism used mayoccur, for example in the form of a slip and/or a belt jump. Inconventional steering systems these unintentional changes in positiontypically lead to a tilted steering wheel when driving straight ahead.In steer-by-wire steering systems or autonomous vehicles without asteering wheel, however, such visual error detection is absent, so thatwithout sufficiently precise detection of the unintentional change inposition safety-critical driving situations can arise. Further problemsarise, for example, when using a steering system with a software endstop for a steering angle. In contrast to a steering system with amechanical end stop, an unintentional change in the position of atraction mechanism may lead to impairment of the functionality of thesoftware end stop and may also lead to mechanical damage to the vehicle,in particular in commercial vehicles with relatively large-sizedelectric motors.

For this reason, for example, in DE 10 2008 021 849 A1 the use set of abelt jump detection device is proposed, which recognizes a belt jump byevaluating a manual torque applied to the steering wheel, a manual angleapplied to the steering wheel and a steering angle of the vehiclewheels. However, a detection of a belt jump on the basis of a detectedmanual torque leads to problems, for example in steer-by-wire steeringsystems or autonomous vehicles without a steering wheel. In addition, inparticular when using a number of belt drives, which of thecorresponding belts has jumped cannot be detected safely, whereby inparticular repair and/or maintenance costs are increased.

Based on this, the object of the invention is in particular to provide amethod and a steering device with improved properties with respect toefficiency. The object is achieved by the features of claims 1, 13 and14, while advantageous embodiments and further developments of theinvention can be taken from the subordinate claims.

DISCLOSURE OF THE INVENTION

The invention is based on a method for monitoring a steering device,wherein the steering device comprises a steering gear, at least onefirst steering actuator, at least one second steering actuator, at leastone first traction mechanism drive with at least one first tractionmechanism for connecting the first steering actuator to the steeringgear and at least one second traction mechanism drive with at least onesecond traction mechanism for connecting the second steering actuator tothe steering gear, and wherein at least one first position parameter ofthe first steering actuator and at least one second position parameterof the second steering actuator is determined.

It is proposed that by evaluating the position parameters, in particularthe first position parameter and the second position parameter, anunintentional change in position of the first traction mechanism and/orthe second traction mechanism is determined, and the unintentionalchange of position is definitely associated with one of the tractionmechanism drives, in particular the first traction mechanism drive orthe second traction mechanism drive. In particular, the unintentionalchange in position of the first traction mechanism and/or the secondtraction mechanism is determined by evaluation of the positionparameters in such a way that the unintentional change of position canbe definitely associated with one of the traction mechanism drives. Bythis design, in particular an efficiency, in particular a maintenanceefficiency, a time efficiency, a component efficiency, a computationalefficiency and/or a cost efficiency can be improved. In addition, inparticular, a particularly robust detection and/or evaluation of theunintentional change in position can be achieved and, in particular, aparticularly high level of operational safety can be guaranteed when asoftware end stop is used for a steering angle. Further, in particularby evaluating the position parameters of the steering actuators, aparticularly high flexibility and/or variability can be achieved, sothat the method may be used advantageously in many different vehicles,in particular with conventional steering systems and/or steer-by-wiresteering systems. In addition, repair and/or maintenance can besimplified in particular by the definite association with one of thetraction mechanism drives.

A “steering device” is to be understood in this context in particular tobe at least one part, in particular a subassembly, a steering system, inparticular of a vehicle, preferably a motor vehicle and particularlypreferably a commercial vehicle. In particular, the steering device mayalso include the entire steering system. In addition, the steeringdevice in particular comprises a computing unit which is provided tocarry out the method for monitoring the steering device. In addition,the steering device may comprise other components and/or assemblies,such as a control unit, a first position sensor unit for detecting thefirst position parameter and/or a second position sensor unit fordetection the second position parameter. The term “provided” is to beunderstood in particular to mean specially programmed, designed and/orequipped. Where an object is provided for a particular function, it isto be understood in particular that the object fulfills and/or carriesout this particular function in at least one application state and/oroperating state.

Furthermore, a “steering actuator” is to be understood in particular tobe an in particular electrically embodied actuator unit, which inparticular has a working connection to the steering gear and inparticular is provided to transfer a steering torque to the steeringgear and thereby to advantageously influence a direction of travel ofthe vehicle. The steering actuator is preferably provided to provide asteering torque to support a manual torque applied to a steering handleand/or a steering torque for automatic and/or autonomous control of adirection of travel of the vehicle. For this purpose, the steeringactuator can comprise at least one electric motor. The electric motor isadvantageously designed as a brushless motor and preferably as anasynchronous motor or as a permanently excited synchronous motor. In thepresent case, the first steering actuator and the second steeringactuator are provided in particular to work together to provide thesteering torque, wherein the first steering actuator and the secondsteering actuator can be operated in particular individually and/oradvantageously simultaneously. Further, a “traction mechanism drive” isto be understood in particular to be a transmission unit with a workingconnection in particular to the first steering actuator and the steeringgear or the second steering actuator and the steering gear, and which isprovided in particular to transfer a driving force and/or a steeringtorque from the first steering actuator or the second steering actuatorto the steering gear. For this purpose, the traction mechanism drivecomprises at least one traction mechanism. In addition, the tractionmechanism drive can comprise in particular at least one drive element,in particular associated with the corresponding steering actuator andadvantageously in the form of a drive wheel and/or a drive shaft, and/orat least one output element, in particular associated with the steeringgear and preferably in the form of an output wheel and/or output shaft.Particularly advantageously, an output element of the first tractionmechanism drive and an output element of the second traction mechanismdrive are identical to each other, in particular such that the firsttraction mechanism and the second traction mechanism are coupled to thesame output element and/or act on the same output element. In addition,the traction mechanism drive could be in the form in particular of aforce-locking traction mechanism drive. Advantageously, however, thetraction mechanism drive is in the form of a positive-locking tractionmechanism drive.

In addition, a “computing unit” is to be understood in particular to bean electrical and/or electronic unit having an information input,information processing and an information output. Advantageously, thecomputing unit further has at least one processor, at least oneoperating memory, at least one input and/or output means, at least oneoperating program, at least one regulation routine, at least one controlroutine, at least one calculation routine and/or at least one evaluationroutine. In particular, the computing unit is provided to determineand/or receive at least one first position parameter of the firststeering actuator and at least one second position parameter of thesecond steering actuator and especially to evaluate these for monitoringthe steering device. In addition, the computing unit is provided inparticular to determine by evaluation of the position parameters anunintentional change in position of the first traction mechanism and/orthe second traction mechanism and to definitely associate theunintentional change in position with one of the traction mechanismdrives. Advantageously, the computing unit is also integrated into thecontrol unit. Furthermore, a “position parameter” is to be understood inparticular to be a parameter which is correlated with a location, inparticular a position, an orientation and/or a condition, of thecorresponding steering actuator and in particular a rotor element of anelectric motor of the corresponding steering actuator. In particular, atleast on the basis of the position parameter a current position of thecorresponding steering actuator and in particular the rotor element canbe concluded and/or a current position of the corresponding steeringactuator and in particular the rotor element can be determined.Preferably, the position parameter is a rotor position and/or an angularposition of the corresponding steering actuator and in particular of therotor element. Further, an “unintentional change in position” of atraction mechanism in particular is to be understood to mean a change inthe position of the traction mechanism, in particular relative to thedrive element, the output element, the corresponding steering actuatorand/or the steering gear, which impairs normal operation of the steeringdevice and/or the vehicle. The unintentional change in position maycorrespond, for example, to clutch slip, slip, in particular slidingslip, and/or a jump of the corresponding traction mechanism.

The first traction mechanism drive and/or the second traction mechanismdrive may be in the form in particular of a chain drive with a tractionmechanism in the form of a chain. However, it is advantageously proposedthat the first traction mechanism drive and/or the second tractionmechanism drive is in the form of a belt drive with a traction mechanismin the form of a belt. In this context, the first traction mechanismand/or the second traction mechanism could be in the form, for example,of flat belts, of round belts, of V-belts and/or of ribbed V-belts.Particularly preferably, however, it is proposed that a toothed belt isused as a traction mechanism. In this case, the first traction mechanismand/or the second traction mechanism is consequently in the form of atoothed belt. Furthermore, the unintentional change of position in thiscase corresponds in particular to a belt jump. Due to this design, inparticular, quiet and low-noise running of the first traction mechanismdrive and/or the second traction mechanism drive and simple maintenanceand/or low maintenance can be achieved.

Furthermore, it is proposed that at least one control parameter of thesteering device is determined, and the evaluation of the positionparameters includes a comparison of the first position parameter and/orthe second position parameter with the control parameter, advantageouslyby forming a difference. A “control parameter” is to be understood inthis context to be in particular a parameter which is correlated with anoutput signal and/or a control signal of the steering gear, which isprovided in particular to change a steering angle of steerable vehiclewheels of the vehicle and/or to cause a steering movement of the vehiclewheels. In particular, at least based on the control parameter, theoutput signal and/or the control signal of the steering gear can beconcluded and/or the output signal and/or the control signal of thesteering gear can be determined. Preferably, in this case the steeringdevice comprises a sensor unit, preferably associated with the steeringgear, with at least one sensor element, in particular in the form of arelative sensor or an absolute sensor, for detecting the controlparameter. Particularly preferably, the control parameter corresponds toa detection signal, in particular in the form of an angle signal, of thesensor unit. As a result, in particular, a particularly simpleevaluation of the position parameters can be achieved, in particularusing a particularly simple computational algorithm.

Furthermore, it is proposed that the control parameter is determined bymeans of a sensor unit associated with the steering gear, in particularthe previously mentioned sensor unit, and a resolution, in particular anangular resolution, of the sensor unit is taken into account in theevaluation of the position parameters. In particular, the resolution ofthe sensor unit can be taken into account at least in determining avalue of the unintentional change in position of the correspondingtraction mechanism and advantageously a number of skipped teeth in atraction mechanism in the form of a toothed belt. Further, inparticular, an evaluation method for evaluating the position parameterscan be adapted and/or varied depending on the resolution of the sensorunit. In particular, a particularly accurate and/or reliable evaluationof the position parameter can be achieved as a result of this.

In a further embodiment, it is proposed that at least one transmissionratio parameter between the first steering actuator and the sensor unitand/or between the second steering actuator and the sensor unit is takeninto account in the evaluation of the position parameters. A“transmission ratio parameter” is to be understood in this context tomean in particular a parameter which is correlated with a transmissionratio, in particular a gear ratio, between the first steering actuatorand the sensor unit and/or between the second steering actuator and thesensor unit. In particular, at least on the basis of the transmissionratio parameter the transmission ratio between the first steeringactuator and the sensor unit and/or between the second steering actuatorand the sensor unit can be concluded and/or the transmission ratiobetween the first steering actuator and the sensor unit and/or betweenthe second steering actuator and the sensor unit can be determined.Advantageously, at least one first transmission ratio parameter betweenthe first steering actuator and the sensor unit and at least one secondtransmission ratio parameter between the second steering actuator andthe sensor unit is taken into account in the evaluation of the positionparameters. Due to this embodiment, in particular a transmission ratioin the steering device can be taken into account, whereby advantageouslya particularly flexible and easily adaptable methodology can beprovided.

A particularly robust method can be provided in particular, if at leastone initial offset parameter is determined at least depending on thefirst position parameter and the sensor parameter and/or depending onthe second position parameter and the sensor parameter and the initialoffset parameter is taken into account in the evaluation of the positionparameters. An “initial offset parameter” is to be understood in thiscontext in particular to mean a parameter which is correlated with aninitial deviation, in particular a deviation occurring and/or applyingat a system start of the steering device, of the steering system and/orof the vehicle, between the first position parameter and the sensorparameter and/or between the second position parameter and the sensorparameter and which is advantageously determined by forming a differenceof a first initial position parameter and an initial control parameterand/or a second initial position parameter and an initial controlparameter. Preferably, the initial offset parameter is determined atregular intervals, such as hourly, daily and/or preferably at eachsystem start. Further, advantageously at least one first initial offsetparameter is determined as a function of the first position parameterand the sensor parameter and at least one second initial offsetparameter is determined as a function of the second position parameterand the sensor parameter and is taken into account in the evaluation ofthe position parameters.

Further, it is proposed that at least one angle segmentation of at leastone output element of the first traction mechanism drive and/or thesecond traction mechanism drive is taken into account in the evaluationof the position parameters. An “angle segmentation” in particular, is tobe understood here to mean an angle between two teeth of the outputelement and/or an angular resolution of the output element. In this way,in particular, a particularly simple evaluation algorithm can beprovided.

Alternatively or additionally, it is proposed that the evaluation of theposition parameters includes a comparison of the first positionparameter with the second position parameter, advantageously by forminga difference. Through this embodiment in particular, a particularlyresource-saving and/or robust evaluation of the position parameters canbe achieved and at the same time operational safety can be increased. Inthis respect, an evaluation of the position parameters can be achievedin particular even if a sensor unit for detecting a control parameter,in particular the aforementioned sensor unit, has too low a resolution,a disturbance and/or a defect and/or if such a sensor unit is dispensedwith.

Further, in particular, a robustness can be increased in this case, ifat least one further initial offset parameter is determined as afunction of the first position parameter and the second positionparameter, and the further initial offset parameter is taken intoaccount in the evaluation of the position parameters. The furtherinitial offset parameter is, in particular analogous to the initialoffset parameter, correlated with an initial deviation, in particular adeviation occurring and/or applying at a system start of the steeringdevice, the steering system and/or the vehicle, between the firstposition parameter size and the second position parameter and isadvantageously determined from the first initial position parameter andthe second initial position parameter by forming a difference. Thefurther initial offset parameter is thereby preferably determined in away analogous to the initial offset parameter and thus advantageously atregular intervals, preferably at each system start.

Further, it is proposed that also in this case at least one anglesegmentation, in particular the aforementioned angle segmentation, atleast of an output element of the first traction mechanism drive and/orof the second traction mechanism drive is taken into account in theevaluation of the position parameters, whereby in particular aparticularly simple evaluation algorithm can be provided.

In addition, it is proposed that the evaluation of the positionparameters and/or the definite association of the unintentional changein position with one of the traction mechanism drives includes acomparison of a first speed parameter of the first steering actuatorwith a second speed parameter of the second steering actuator. A “speedparameter” is in particular to be understood to mean a parameter whichis correlated with a speed, in particular an operating speed, of thecorresponding steering actuator and in particular of a rotor element ofan electric motor of the corresponding steering actuator. In particular,at least based on the speed parameter a current speed of thecorresponding steering actuator and in particular of the rotor elementcan be concluded and/or a current speed of the corresponding steeringactuator and in particular of the rotor element can be determined.Preferably, the speed parameter is a rotor speed and/or an angularvelocity of the corresponding steering actuator and in particular of therotor element. In addition the first speed parameter is preferablydetermined by means of a differentiation of the first position parameterand/or the second speed parameter is preferably determined by means of adifferentiation of the second position parameter. As a result of this,in particular, a particularly simple and/or cost-effective associationof the unintentional change in position with one of the tractionmechanism drives can be achieved.

The method for monitoring the steering device, the control unit and thesteering device should not be limited to the application and embodimentdescribed above. In particular, the method for monitoring the steeringdevice, the control unit and the steering device for the fulfillment ofa mode of operation described herein can have a different number ofindividual elements, components and units from the number mentionedherein.

DRAWINGS

Further advantages result from the following description of thedrawings. In the drawings, an exemplary embodiment of the invention isshown. The drawings, the description and the claims contain numerousaspects of the invention. The person skilled in the art will considerthese aspects expediently and individually and will combine them intomeaningful further combinations.

In the figures:

FIG. 1 shows at least part of a steering system with an exemplarysteering device in a schematic illustration and

FIG. 2 shows an exemplary flowchart of a method for monitoring thesteering device.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 shows at least one part of a steering system 32 with an exemplarysteering device in a schematic representation. The steering system 32 isin the present case in the form of an electrically assisted steeringsystem. Further, the steering system 32 is provided for use in a vehicle(not shown), advantageously a commercial vehicle. When installed, thesteering system 32 has a working connection to vehicle wheels of thevehicle and is provided to influence a direction of travel of thevehicle. Further, the steering system 32 can be in the form of aconventional steering system with a mechanical feedthrough or of aso-called steer-by-wire steering system, in which a steering command isforwarded exclusively electrically to the vehicle wheels. In addition,the steering system 32 in the present case may include in particular asoftware end stop for a steering angle. Alternatively, however, avehicle could also be in the form of a passenger car or the like. Inaddition, it is conceivable to dispense with a software end stop and,for example, to use a mechanical end stop.

The steering device has a steering gear 10. The steering gear 10 is inthe present case in the form of a known steering gear 10, in particulara commercial vehicle steering gear. The steering gear 10 has a workingconnection to at least two of the vehicle wheels, in particularsteerable vehicle wheels and advantageously front wheels of the vehicle.The steering gear 10 is provided to provide an output signal and/or acontrol signal to cause a pivoting movement and/or a rotary movement ofthe vehicle wheels.

Further, the steering device has a number of steering actuators 12, 14,in the present case in particular a first steering actuator 12 and asecond steering actuator 14. The steering actuators 12, 14 are formedseparately from each other and arranged at a distance from each other.The steering actuators 12, 14 are designed for example to be identicalto each other. In principle, however, it is also conceivable to designsteering actuators 12, 14 differently. In addition, the steeringactuators 12, 14 each have a working connection to the steering gear 10.Each of the steering actuators 12, 14 is provided to provide a steeringtorque for generating and/or influencing the output signal and/or thecontrol signal of the steering gear 10 and to transmit this to thesteering gear 10. In the present case, the steering actuators 12, 14 areprovided to work together to provide a total steering torque, wherein inparticular the steering actuators 12, 14 are operated simultaneously.

For this purpose, each of the steering actuators 12, 14 has at least oneelectric motor 34, 36. The electric motors 34, 36 are in the form ofrotary motors and each has a rotor element (not shown). The electricmotors 34, 36 are in the present case in the form of permanently excitedsynchronous motors. In principle, however, at least one of the electricmotors 34, 36 could also be in the form of another electric motor whichis different from a permanently excited synchronous motor. Further, atleast one of the steering actuators 12, 14 could also comprise a numberof electric motors or an electric motor with a number of separate and/orseparately energizable windings.

For connecting the steering actuators 12, 14 to the steering gear 10,the steering device further comprises a number of traction mechanismdrives 16, 20, in the present case in particular a first tractionmechanism drive 16 for connecting the first steering actuator 12 to thesteering gear 10 and a second traction mechanism drive 20 for connectingthe second steering actuator 14 to the steering gear 10. The tractionmechanism drives 16, 20 are formed separately from each other. Thetraction mechanism drives 16, 20 are for example structurally identicalto each other and consequently have in particular the same tractionmechanism transmission ratio. In principle, however, it is alsoconceivable to design the traction mechanism drives 16, 20 differently.The traction mechanism drives 16, 20 are in the present case each in theform of a belt drive. Further, the traction mechanisms drives 16, 20 areeach in the form of a positive-locking traction mechanism drive. Thetraction mechanism drives 16, 20 are each provided to transfer thesteering torque of the corresponding steering actuator 12, 14 to thesteering gear 10. Alternatively however, at least one of the tractionmechanism drives 16, 20 could also be in the form of a chain driveand/or a force-locking traction mechanism drive.

The first traction mechanism drive 16 comprises a first drive element 38associated with the first steering actuator 12 and in the form of adrive shaft. The first drive element 38 is formed separately from thefirst steering actuator 12 and is attached to it. In principle, however,a first drive element could also be formed in one piece with a firststeering actuator. In addition, the first traction mechanism drive 16has an output element 26 associated with the steering gear 10 and in theform of an output wheel. In addition, the first traction mechanism drive16 has a first traction mechanism 18. The first traction mechanism 18 isin the form of a belt, in the present case in particular of a toothedbelt. The first traction mechanism drive 18 connects the first driveelement 38 and the output element 26 to each other. The first tractionmechanism 18 connects the first drive element 38 and the output element26 together and is used for force transmission between the first driveelement 38 and the output element 26.

The second traction mechanism drive 20 comprises a second drive element40 associated with the second steering actuator 14 and in the form of adrive shaft. The second drive element 40 is formed separately from thesecond steering actuator 14 and is attached to it. In principle,however, a second drive element could also be formed in one piece with asecond steering actuator. An output element of the second tractionmechanism drive 20 is identical with the output element 26 of the firsttraction mechanism drive 16. In addition, the second traction mechanismdrive 20 has a second traction mechanism 22. The second tractionmechanism 22 is in the form of a belt, in the present case in particularof a toothed belt. The second traction mechanism 22 connects the seconddrive element 40 and the output element 26 to each other and is used forforce transmission between the second drive element 40 and the outputelement 26. Alternatively, it is also conceivable to design at least oneof the traction mechanisms 18, 22 as flat belts, as a round belt, as aV-belt and/or as a ribbed V-belt. In addition, an output element of afirst traction mechanism drive and an output element of a secondtraction mechanism drive could be formed differently and/or separatelyfrom each other.

In addition, the steering device comprises a number of position sensorunits 42, 44, in particular a first position sensor unit 42 associatedwith the first steering actuator 12 and a second position sensor unit 44associated with the second steering actuator 14. The position sensorunits 42, 44 are identical to each other and each is in the form of arelative sensor. In the present case, the position sensor units 42, 44are each in the form of a rotor position sensor. The first positionsensor unit 42 is provided for detecting a first position parameter α₁of the first steering actuator 12. The first position parameter α₁corresponds in the present case to a rotor position and/or an angularposition of the first steering actuator 12. The second position sensorunit 44 is provided for detecting a second position parameter α₂ of thesecond steering actuator 14. The second position parameter α₂corresponds in the present case to a rotor position and/or an angularposition of the second steering actuator 14. In principle, however, itis also conceivable to dispense with at least one of the position sensorunits 42, 44. In addition, a position parameter could also correspond toa variable of a corresponding steering actuator which is different froma rotor position and/or an angular position. Furthermore, it isconceivable to design at least one position sensor unit as an absolutesensor.

Furthermore, the steering device in the present case has a sensor unit24 associated with the steering gear 10. The sensor unit 24 is in theform of an absolute sensor. The sensor unit 24 is in the form of acombined torque and rotation angle sensor. The sensor unit 24 isprovided for detecting a control parameter α_(s) of the steering device,which in particular is correlated with the output signal and/or thecontrol signal of the steering gear 10. In principle, however, thesensor unit 24 could be dispensed with. In addition, it is conceivableto design a sensor unit as a sensor which is different from a combinedtorque and rotation angle sensor, for example as a purely torque sensoror rotation angle sensor, and/or as an absolute sensor.

Further, the steering device has at least one control unit 28. Thecontrol unit 28 has a working connection to the steering actuators 12,14 and/or the position sensor units 42, 44. In addition, the controlunit 28 has a working connection to the steering gear 10 and/or thesensor unit 24. The control unit 28 is at least provided to receive andevaluate the first position parameter α₁ and the second positionparameter α₂. In addition, the control unit 28 is provided in thepresent case to receive and evaluate the control parameter α_(s).

For this purpose, the control unit 28 comprises a computing unit 30. Thecomputing unit 30 comprises at least one processor (not shown), forexample in the form of a microprocessor, and at least one operatingmemory (not shown). In addition, the computing unit 30 comprises atleast one operating program located in the operating memory with atleast one calculation routine, at least one control routine and at leastone evaluation routine. In principle, however, it is also conceivable toform a control unit separately from a steering device. In this context,a vehicle could, for example, have a single central control unit with acentral computing unit. Further, a steering device could comprise anumber of, in particular separate, control units and/or a number of, inparticular separate, computing units, which in particular can becommunicatively connected to each other. In this context, for example,it is conceivable to associate each steering actuator with a dedicatedcontrol unit.

With the use of traction mechanism drives, such as the tractionmechanism drives 16, 20 referred to at the beginning, there is theproblem that in operation and under certain conditions unintentionalchanges in position of the corresponding traction mechanism can occur,in the present case in particular in the form of a belt jump. Suchunintentional changes in position can lead to safety-critical drivingsituations without sufficiently precise detection. Furthermore, inparticular with the use of a number of traction mechanism drives, repairand/or maintenance costs are significantly reduced if the unintentionalchange in position can be definitely associated with one of the tractionmechanism drives.

For the determination and association of such unintentional changes inthe position of the traction mechanism 18, 22 of the traction mechanismdrives 16, 20, a method for monitoring the steering device is thereforeproposed. In the present case, in particular, the computing unit 30 isprovided, in particular by means of the calculation routine and/or theevaluation routine, to carry out the method and in particular has acomputer program with corresponding program code means for this purpose.

According to the invention, for monitoring the steering device the firstposition parameter α₁ of the first steering actuator 12 and the secondposition parameter α₂ of the second steering actuator 14 are determined.By evaluating the position parameters α₁, α₂, an unintentional change inposition, in the present case in particular a belt jump, of the firsttraction mechanism 18 and/or the second traction mechanism 22 is thendetermined and definitely associated with one of the traction mechanismdrives 16, 20.

The evaluation of the position parameters α₁, α₂ can also be carried outin the present case by means of two different evaluation methods, whichin particular can also be combined with each other, whereby inparticular a particularly safe and/or robust evaluation can be achieved.

According to a first evaluation method, in particular in addition to theposition parameters α₁, α₂, the control parameter α_(s) is determined bythe steering device by means of the sensor unit 24. In this case, theevaluation of the position parameters α₁, α₂ includes a comparison ofthe first position parameter α₁ with the control parameter as and acomparison of the second position parameter α₂ with the controlparameter α_(s). For this purpose, the following inequalities are used:

$\begin{matrix}{{{{{\alpha_{1} \cdot i_{G}} - \alpha_{s}}} - \Delta_{{LS}\; 1}} > {\left( {{WS} \cdot \frac{i_{G}}{i_{Z}}} \right) \cdot x}} & (1) \\{{{{{{\alpha_{2} \cdot i_{G}} - \alpha_{s}}} - \Delta_{{LS}\; 2}} > {\left( {{WS} \cdot \frac{i_{G}}{i_{Z}}} \right) \cdot y}}{with}} & (2) \\{i_{G} = \frac{i_{Z} \cdot i_{LG}}{i_{s}}} & (3) \\{\Delta_{{LS}\; 1} = {{{\alpha_{1,{init}} \cdot i_{G}} - \alpha_{s,{init}}}}} & (4) \\{\Delta_{{LS}\; 2} = {{{\alpha_{2,{init}} \cdot i_{G}} - \alpha_{s,{init}}}}} & (5) \\{{WS} = \frac{360{^\circ}}{n}} & (6)\end{matrix}$

The variable i_(G) describes a transmission ratio between the firststeering actuator 12 and the sensor unit 24 and/or between the secondsteering actuator 14 and the sensor unit 24 and defines in the presentcase a transmission ratio parameter between the first steering actuator12 and the sensor unit 24 and/or between the second steering actuator 14and the sensor unit 24. Further, i_(z) describes the traction mechanismtransmission ratio of the two traction mechanism drives 16, 20, whereinin this case, for the sake of simplification, it is assumed that thetraction mechanism transmission ratios of the traction mechanism drives16, 20 are identical (i_(z1)=i_(z2)=i_(z)). Furthermore, i_(LG)describes a transmission ratio of the steering gear 10 and is describesa transmission ratio of the sensor unit 24. Accordingly, in theevaluation of the position parameters α₁, α₂ at least one transmissionratio parameter between the first steering actuator 12 and the sensorunit 24 and/or between the second steering actuator 14 and the sensorunit 24 is taken into account. In principle, a traction mechanismtransmission ratio of a first traction mechanism drive and a secondtraction mechanism drive may also differ from each other, whereby inparticular a transmission ratio between a first steering actuator and asensor unit and between a second steering actuator and a sensor unit mayalso differ from each other.

The variable Δ_(LS1) describes a first initial offset parameter and isdetermined as a function of the first position parameter α₁ and thesensor parameter α_(s). In the present case, the first initial offsetparameter Δ_(LS1) is determined by forming a difference of a firstinitial position parameter α_(1,init) and an initial control parameterα_(s,init), wherein the first initial position parameter α_(1,init) andthe initial control variable α_(s,init) and consequently the firstinitial offset parameter Δ_(LS1) will advantageously be determined ateach system start. The same applies to the variable Δ_(LS2), whichdescribes a second initial offset parameter and which is determined as afunction of the second position parameter α₂ and the sensor parameterα_(s). The second initial offset parameter Δ_(LS2) is determined byforming a difference of a second initial position parameter α_(2,init)and the initial control parameter α_(s,init), wherein the second initialposition parameter α_(2,init) and the initial control parameterα_(s,init) and consequently the second initial offset parameter Δ_(LS2)are advantageously determined at each system start. Consequently, in theevaluation of the position parameters α₁, α₂ at least one initial offsetparameter, in particular the first initial offset parameter Δ_(LS1) andthe second initial offset parameter Δ_(LS2), is taken into account.Alternatively, at least one initial offset parameter could also bedetermined only once, in particular during manufacture and/or assemblyof a steering device, and stored, for example, in the event of ashutdown and/or an absolute shutdown of the steering device. In thiscontext, the steering device and/or a computing unit in particular couldalso include a so-called “sleep mode counter”, which is provided tomonitor changes of a first position parameter, a second positionparameter and/or a control parameter at least in an inactive stateand/or a switched off state of the steering device.

The variable WS defines an angle segmentation of the output element 26and thus describes an angle between two teeth of the output element 26and/or an angular resolution of the output element 26. In particular, ndescribes a number of teeth of the output element 26. Accordingly, inthe evaluation of the position parameters α₁, α₂ at least one anglesegmentation of the output element 26 is taken into account.Alternatively, however, it is also conceivable to relate the variable WSor the corresponding equations to the drive element 38, 40.

Furthermore, the variables x and y define pre-applied values and aredetermined once according to the following equations:

$\begin{matrix}{x = \left\lceil \frac{k_{s}}{{WS}\frac{i_{C}}{i_{Z}}} \right\rceil} & (7) \\{y = \left\lceil \frac{k_{s}}{{WS}\frac{i_{C}}{i_{Z}}} \right\rceil} & (8) \\{where} & \; \\{w = {\lbrack z\rbrack:={\min\left\{ {{w \in {\mathbb{Z}}}❘{w \geq z}} \right\}}}} & (9)\end{matrix}$

describes the so-called rounding up function. In addition, k_(s)describes a resolution, in particular an angular resolution, of thesensor unit 24. Accordingly, in the evaluation of the positionparameters α₁, α₂ at least one resolution of the sensor unit 24 is takeninto account.

For example, with an exemplary resolution of the sensor unit 24 ofk_(s)=1°, a transmission ratio i_(G)/i_(Z) of i_(G) =7 and a number ofteeth of the output element 26 of n=70 apply:

$\begin{matrix}{\mspace{79mu}{x,{y = {\left\lceil \frac{1{^\circ}}{\text{?}} \right\rfloor = {\lbrack 0.0278\rbrack = 1}}}}} & \; \\{\text{?}\text{indicates text missing or illegible when filed}} & \;\end{matrix}$

The number of skipped teeth N₁,N₂ which can be detected, in particularin the context of the resolution of the sensor unit 24, can then beestimated in the context of the resolution of the sensor unit 24 as anintegral multiple of x and/or y and/or can be calculated using thefollowing equations:

$\begin{matrix}{{{{{\alpha_{1} \cdot i_{G}} - \alpha_{s}}} - \Delta_{{LS}\; 1}} = {\left( {{WS} \cdot \frac{i_{G}}{i_{Z}}} \right) \cdot x \cdot N_{1}}} & (10) \\{{{{{\alpha_{2} \cdot i_{G}} - \alpha_{s}}} - \Delta_{{LS}\; 2}} = {\left( {{WS} \cdot \frac{i_{G}}{i_{Z}}} \right) \cdot y \cdot N_{2}}} & (11)\end{matrix}$

On the basis of inequalities (1) and (2) or equations (10) and (11)and/or a comparison of inequalities (1) and (2) or equations (10) and(11) with each other, the unintentional change in position can bedefinitely associated with the first traction mechanism drive 16 or thesecond traction mechanism drive 20. Further, at least when using atraction mechanism 18, 22 in the form of a toothed belt and in thecontext of the resolution of the sensor unit 24, the number of skippedteeth N₁,N₂ can be specified.

According to a second evaluation method, which can be combined inparticular with the first evaluation method, the evaluation of theposition parameters α₁, α₂ includes a comparison of the first positionparameter α₁ with the second position parameter α₂. By this evaluationmethod, an evaluation of the position parameters α₁, α₂ in particularcan also be achieved when the sensor unit 24 has too low a resolution, adisturbance and/or a defect and/or when such a sensor unit is dispensedwith. For this purpose, the following inequality is used:

|α₁−α₂|−Δ_(LL) >WS  (12)

with

Δ_(LL)=|α_(1,init)−α_(2,init)|  (13)

The variable Δ_(LL) describes another initial offset parameter and isdetermined as a function of the first position parameter α₁ and thesecond position parameter α₂. In the present case, the further initialoffset parameter Δ_(LL) is determined by forming a difference of thefirst initial position parameter α_(2,init) and the second initialposition parameter α_(2,init), wherein the first initial positionparameter α_(2,init) and the second initial position parameterα_(2,init) and consequently the further initial offset parameter Δ_(LL)are advantageously determined at each system start. Consequently, inthis case, at least one initial offset parameter, in particular thefurther initial offset parameter Δ_(LL), is taken into account in theevaluation of the position parameters α₁, α₂. Alternatively, the furtherinitial offset parameter Δ_(LL) could also be determined only once, inparticular during manufacture and/or assembly of a steering device, and,for example, in the event of a shutdown and/or an absolute shutdown ofthe steering device. In this context, the steering device and/or acomputer unit could also contain in particular a so-called “sleep modecounter”, which is provided to monitor changes of a first positionparameter and/or a second position parameter at least in an inactivestate and/or a switched off state of the steering device.

The variable WS again defines the angle segmentation of the outputelement 26. Consequently, in this case, too, at least one anglesegmentation of the output element 26 is taken into account in theevaluation of the position parameters α₁, α₂.

By the inequality (12), the presence of an unintentional change inposition of the first traction mechanism 18 and/or the second tractionmechanism 22 can be determined.

In order further to achieve a definite association of the unintentionalchange in position with the first traction mechanism drive 16 or thesecond traction mechanism drive 20, a comparison is also carried of afirst speed parameter v₂ of the first steering actuator 12 with a secondspeed parameter v₂ of the second steering actuator 14. In the presentcase, a difference between a magnitude of the first speed parameter v₂and a magnitude of the second speed parameter v₂ is formed and iscompared with a pre-applied threshold value T_(v), wherein the thresholdvalue T_(v) is adapted and/or selected in particular depending on adesign of the steering device. Where:

|ν₁|−|ν₂ |≥T _(ν)  (14)

|ν₁|−ν₂ |<T _(ν)  (15)

If the difference between the magnitude of the first speed parameter v₂and the magnitude of the second speed parameter v₂ is greater than orequal to the threshold value T_(v) or if the inequality (14) issatisfied, it can be concluded from this that the unintentional changein position occurred in the first traction mechanism drive 16. However,if the difference between the magnitude of the first speed parameter v₂and the magnitude of the second speed parameter v₂ is less than thethreshold value T_(v) or if the inequality (15) is satisfied, it can beconcluded that the unintentional change in position occurred in thesecond traction mechanism drive 20.

Consequently, by the evaluation of the inequalities (12), (14) and (15),the unintentional change in position can be definitely associated withthe first traction mechanism drive 16 or the second traction mechanismdrive 20.

The first speed parameter v₂ corresponds in the present case further toa rotor speed and/or an angular velocity of the first steering actuator12. Analogously, the second speed parameter v₂ corresponds to a rotorspeed and/or an angular velocity of the second steering actuator 14.Preferably, the first speed parameter v₂ is determined by means of adifferentiation of the first position parameter α₁ and the second speedparameter v₂ is determined by means of a differentiation of the secondposition parameter α₂, whereby advantageously additional speed sensorunits can be dispensed with. In principle, however, it is alsoconceivable to determine at least one of the speed parameters v₁,v₂ bymeans of a speed sensor unit.

An exemplary flowchart of the method for monitoring the steering deviceis shown in FIG. 2.

In a step 50 of the method, the first position parameter α₁ of the firststeering actuator 12 and the second position parameter α₂ of the secondsteering actuator 14 are determined.

In a step 52 of the method, in particular in addition to the positionparameters α₁, α₂, the control parameter α_(s) of the steering device isdetermined by means of the sensor unit 24.

In a step 54 of the method, using the first evaluation method, the firstposition parameter α₁ is compared with the control parameter α_(s) andthe second position parameter α₂ is compared with the control parameterα_(s). If an unintentional change in position, in the present case inparticular a belt jump, of the first traction mechanism 18 and/or thesecond traction mechanism 22 is determined, a step 56 of the methodfollows. If, on the other hand, no unintentional change in the positionof the first traction mechanism 18 and/or the second traction mechanism22 is determined, a step 58 of the method follows.

In the step 56 of the method, in particular by the inequalities (1) and(2) or the equations (10) and (11) and/or a comparison of theinequalities (1) and (2) or the equations (10) and (11) with each other,the unintentional change in position is definitely associated with thefirst traction mechanism drive 16 or the second traction mechanism drive20. Subsequently, for example, a warning message can be generated and/ora fail-safe mode of the vehicle can be initiated.

In the step 58 of the method, the evaluation method is changed from thefirst evaluation method to the second evaluation method.

In the step 60 of the method, using the second evaluation method, thefirst position parameter α₁ is compared with the second positionparameter α₂. As a result of this, an evaluation of the positionparameters α₁, α₂, in particular can also then be achieved when thesensor unit 24 has too low a resolution, a disturbance and/or a defect.If an unintentional change in position, in the present case inparticular a belt jump, of the first traction mechanism 18 and/or thesecond traction mechanism 22 is determined, then a step 62 of the methodand a step 64 of the method follow. If, on the other hand, nounintentional change in the position of the first traction mechanism 18and/or the second traction mechanism 22 is determined, a step 66 of themethod follows.

In the step 62 of the method, a first speed parameter v₂ of the firststeering actuator 12 is determined, in particular by differentiating thefirst position parameter α₁, and a second speed parameter v₂ of thesecond steering actuator 14 is determined, in particular bydifferentiating the second position parameter α₂.

Subsequently, in the step 64 of the method, the first speed parameter v₂is compared with the second speed parameter v₂, in order to achieve, inparticular by means of the inequalities (14) and (15), a definiteassociation of the unintentional change in position with the firsttraction mechanism drive 16 or the second train medium drive 20.Thereupon, for example, a warning message can be generated and/or afail-safe mode of the vehicle can be initiated.

In the step 66 of the method, the method is terminated, and it isdetermined that at least in the context of the present evaluationmethodology no unintentional change in position of the first tractionmechanism 18 and/or the second traction mechanism 22 has taken place.

The exemplary flowchart in FIG. 2 is provided in particular to describea method for monitoring the steering device only by way of example. Inparticular, individual steps of the method and/or a sequence of thesteps of the method may also vary. In particular, it is also conceivableto omit steps 52, 54 and 56 of the method or steps 58, 60, 62 and 64 ofthe method. In addition, further optional steps of the method could beadded.

1. A method for monitoring a steering device, wherein the steeringdevice comprises a steering gear, at least one first steering actuator,at least one second steering actuator, at least one first tractionmechanism drive with at least one first traction mechanism configured toconnect the at least one first steering actuator to the steering gear,and at least one second traction mechanism drive with at least onesecond traction mechanism configured to connect the at least one secondsteering actuator to the steering gear, comprising: determining at leastone first position parameter of the first steering actuator; determiningat least one second position parameter of the second steering actuator;evaluating the at least one first position parameters and the at leastone second position parameter; determining that an unintentional changein position of at least one of the at least one first traction mechanismand the at least one second traction mechanism has occurred based uponthe evaluation; and definitely associating the unintentional change inposition with one of the at least one first traction mechanism drivesand at least one second traction mechanism drives.
 2. The method asclaimed in claim 1, wherein: the at least one first traction mechanismcomprises a first toothed belt; the at least one second tractionmechanism comprises a second toothed belt; and the unintentional changein position is a belt jump.
 3. The method as claimed in claim 1, furthercomprising: determining at least one control parameter of the steeringdevice, wherein the evaluation of the at least one first positionparameter and the at least one second position parameter includes:comparing at least one of the at least one first position parameter andthe at least one second position parameter with the determined at leastone control parameter.
 4. The method as claimed in claim 3, whereindetermining the at least one control parameter comprises: using a sensorunit associated with the steering gear to determine the at least onecontrol parameter, and a resolution of the sensor unit is taken intoaccount in the evaluation of the at least one first position parameterand the at least one second position parameter.
 5. The method as claimedin claim 4, wherein at least one transmission ratio parameter between atleast one of the at least one first steering actuator and the sensorunit, and between the at least one second steering actuator and thesensor unit, is taken into account in the evaluation of the at least onefirst position parameter and the at least one second position parameter.6. The method as claimed in claim 4, wherein at least one initial offsetparameter is determined depending on at least one of the at least onefirst position parameter and the sensor, and the second at least oneposition parameter and the sensor, and the at least one initial offsetparameter is taken into account in the evaluation of the at least onefirst position parameters and the at least one second positionparameter.
 7. The method as claimed in claim 3, wherein at least oneangle segmentation of at least one output element of the at least onefirst traction mechanism drive and the at least one second tractionmechanism drive is taken into account in the evaluation of the at leastone first position parameter and the at least one second positionparameter.
 8. The method as claimed in claim 1, wherein the evaluationof the at least one first position parameter and the at least one secondposition parameter includes a comparison of the at least one firstposition parameter with the at least one second position parameter. 9.The method as claimed in claim 8, wherein at least one further initialoffset parameter is determined as a function of the at least one firstposition parameter and the at least one second position parameter, andthe at least one further initial offset parameter is taken into accountin the evaluation of the at least one first position parameter and theat least one second position parameter.
 10. The method as claimed inclaim 8, wherein at least one angle segmentation of at least one outputelement of the at least one first traction mechanism drive and the atleast one second traction mechanism drive is taken into account in theevaluation of the at least one first position parameters and the atleast one second position parameter.
 11. The method as claimed in claim8, wherein the evaluation of the at least one first position parameterand the at least one second position parameter includes a comparison ofa first speed parameter of the first steering actuator with a secondspeed parameter of the second steering actuator.
 12. The method asclaimed in claim 11, wherein the at least one first speed parameter isdetermined using a differentiation of the at least one first positionparameter, and the at least one second speed parameter is determinedusing a differentiation of the at least one second position parameter.13. A control unit with a computing unit configured to preform themethod as claimed in claim
 1. 14. A steering device with a steeringgear, with at least one first steering actuator, with at least onesecond steering actuator, with at least one first traction mechanismdrive which comprises at least one first traction mechanism configuredto connect the first steering actuator to the steering gear, with atleast one second traction mechanism drive which comprises at least onesecond traction mechanism configured to connect the second steeringactuator to the steering gear, and with a computing unit configured toperform the method as claimed in claim 1.